Add #wait_readable and #wait_writable to IO::FileDescriptor and Socket

src/crystal/system/file_descriptor.cr

@@ -39,6 +39,14 @@ module Crystal::System::FileDescriptor
     event_loop.write(self, slice)
   end
 
+  private def system_wait_readable : Nil
+    event_loop.wait_readable(self)
+  end
+
+  private def system_wait_writable : Nil
+    event_loop.wait_writable(self)
+  end
+
   private def event_loop? : Crystal::EventLoop::FileDescriptor?
     Crystal::EventLoop.current?
   end

src/crystal/system/socket.cr

@@ -89,6 +89,14 @@ module Crystal::System::Socket
     event_loop.write(self, slice)
   end
 
+  private def system_wait_readable : Nil
+    event_loop.wait_readable(self)
+  end
+
+  private def system_wait_writable : Nil
+    event_loop.wait_writable(self)
+  end
+
   # private def system_close
 
   # Closes the internal handle without notifying the event loop.

src/io/file_descriptor.cr

@@ -315,4 +315,18 @@ class IO::FileDescriptor < IO
   private def unbuffered_flush : Nil
     # Nothing
   end
+
+  # Blocks the current fiber until the file descriptor is ready for read.
+  # Raises `TimeoutError` when the configured `#read_timeout` has elapsed,
+  # otherwise returns normally.
+  def wait_readable : Nil
+    system_wait_readable
+  end
+
+  # Blocks the current fiber until the file descriptor is ready for write.
+  # Raises `TimeoutError` when the configured `#write_timeout` has elapsed,
+  # otherwise returns normally.
+  def wait_writable : Nil
+    system_wait_writable
+  end
 end

src/socket.cr

@@ -467,6 +467,20 @@ class Socket < IO
   private def unbuffered_flush : Nil
     # Nothing
   end
+
+  # Blocks the current fiber until the socket is ready for read. Raises
+  # `TimeoutError` when the configured `#read_timeout` has elapsed, otherwise
+  # returns normally.
+  def wait_readable : Nil
+    system_wait_readable
+  end
+
+  # Blocks the current fiber until the socket is ready for write. Raises
+  # `TimeoutError` when the configured `#write_timeout` has elapsed, otherwise
+  # returns normally.
+  def wait_writable : Nil
+    system_wait_writable
+  end
 end
 
 require "./socket/*"